The 25-year old forward has been heavily linked with a loan move with the view to a permanent deal to homeland club Millonarios recently and he has given the clearest indication yet that a shift is close to being complete.
"I want to thank god for these 4 unforgettable years in seattle, to the sounders staff, couches, players and especially the FANS for everything you gave me," he posted.
"You guys are all truly remarkable. Thanks Adrian (Hanauer) for your unconditional support.
"Seattle you will always be in my heart and be my second home. I will be back one day!
"Until then I wish you all the best. God bless."
Montero also changed his Twitter profile to read 'Ex Seattle Sounders FC player' suggesting the deal had been done.